The disclosure relates generally to optical fiber spans comprising optical fiber pairs and more specifically to optical fiber spans comprising optical fiber pairs for low DMD applications.
The explosive growth in the volume and variety of multi-media telecommunication applications continues to drive speed demands for internet traffic and motivate research in long-haul fiber-optic telecommunication.
Modern high-data-rate coherent transmission systems are already approaching information capacity limits. To exploit the full capacity in optical fiber, advanced multi-level modulation formats, such as QAM, and/or superchannel or OFDM systems will be needed. However these systems require higher signal-to-noise ratios (SNR) than are currently feasible. Fiber nonlinearities and fiber attenuation are the key performance limitations that prevent the higher SNRs from being achieved.
Compared to ordinary single-mode fibers, large effective area fibers are desirable because they can carry more optical power before the onset of nonlinear propagation impairments. However, to achieve extremely large effective areas (Aeff>>140 μm2) with low bend loss, these large effective area fibers are often multimoded. Thus, they typically can introduce modal dispersion into the fiber spans. Modal dispersion is the spreading of pulses due to the different velocities of the modes. In such fibers, the light propagates in many different modes within in the fiber core. A “mode” is an allowable path for the light to travel through the fiber core. A multimode fiber allows many light propagation paths within its core, while a single-mode fiber allows only one light path. In a multimode fiber, the time it takes for light to travel through the fiber core is different for each mode, resulting in a spreading of the pulse at the output of the fiber. The difference in the time delay between modes is the called Differential Mode Delay (MID). Modal dispersion limits the bandwidth of optical fiber spans, limiting fiber span's information carrying capacity, i.e., how far a transmission system can operate at a specified bit error rate. Typically, as the fiber's effective area increases, deleterious nonlinear distortions decrease, but the number of supported modes, and hence the modal dispersion increases, making it difficult to achieve the desired system performance.
One solution is to utilize only large effective area fibers that have essentially no DMD over a wide wavelength range, but such fiber designs would be difficult and expensive to make in practice, and if such fibers are made they would have be made to very tight manufacturing tolerances.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinence of any cited documents.